The central auditory system of mammals consists of a number of parallel pathways which converge and diverge from one another in complex ways that are not fully understood. The overall objective of the proposed research is to study the neural basis for hearing by using neuroanatomical and behavioral methods to discover differences in these pathways. It is proposed to examine connections of ascending auditory pathways in the brain stem of mammals, especially pathways ascending from the cochlear nucleus and superior olivary complex to the inferior colliculus. Particular emphasis will be placed on how these pathways converge and diverge from one another. The anatomical methods include techniques for tracing transported molecules. Intracellular injection of horseradish peroxidase will be used to trace the connections of single neurons. Behavioral studies will focus on the role of the different auditory pathways in auditory discrimination, especially localization of sound in space. For example tests of the ability of animals to localize sound will be made before and after lesions in subdivisions of the cochlear nucleus or in subdivisions of the superior olivary complex. These studies will shed light on the functional significance of the different auditory pathways.